Apparent differential response of nuclear envelope cytochrome P-450 following phenobarbital induction arising from a preferential loss during gradient purification.
We have investigated the response of rat liver nuclear, nuclear envelope, and microsomal cytochrome P-450 (or P-448) to various treatments. Responses of these subcellular fractions to 3-methylcholanthrene pretreatment were generally similar. In endoplasmic reticulum preparations, we observed an increase in cytochrome P-450 content following phenobarbital pretreatment, which was reduced by subsequent thioacetamide treatment. Nuclear envelope cytochrome P-450 was apparently not modulated by these treatments, although nuclear cytochrome P-450 content was increased by phenobarbital. When endoplasmic reticulum preparations were subjected to treatments paralleling those used in nuclear envelope purification, we found a preferential loss of cytochrome P-450 from phenobarbital-pretreated preparations, with a loss of camphor-binding ability. The data point to potential problems with use of isolated nuclear envelopes as a representative model for nuclear metabolism of carcinogens, including low total recoveries and enrichments, and the potential for selective or differential recovery of cytochrome P-450 populations following various modes of induction or reduction.
D000818:Animals; D002458:Cell Fractionation / Q000379:methods; D002499:Centrifugation, Density Gradient / Q000379:methods; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D003580:Cytochromes / Q000378:metabolism; D015786:Cytochromes b5; D004790:Enzyme Induction / Q000187:drug effects; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology; D006899:Mixed Function Oxygenases / Q000378:metabolism; D009251:NADPH-Ferrihemoprotein Reductase / Q000378:metabolism; D009685:Nuclear Envelope / Q000201:enzymology*; D010634:Phenobarbital / Q000494:pharmacology*; D051381:Rats; D014468:Umbelliferones / Q000378:metabolism
D003580:Cytochromes; D014468:Umbelliferones; D008748:Methylcholanthrene; D015786:Cytochromes b5; D003577:Cytochrome P-450 Enzyme System; D006899:Mixed Function Oxygenases; D009251:NADPH-Ferrihemoprotein Reductase; D010634:Phenobarbital